This invention relates to head unit for a press that is used to install pierce nuts onto a panel. The head unit of the present invention provides an improved mechanism for ensuring precise relative movement between the stationary and movable members while providing an inexpensive and simple mechanism which facilitates replacing worn head unit components.
Prior art head units typically utilized a pair of guide pins, or shoulder screws to ensure that the movable and stationary members were properly aligned and to retain the movable member as the spring biased the movable member away from the stationary member. The guide pins were received in bores in the movable member and threaded into the stationary member. One such head unit is disclosed in U.S. Pat. No. 4,505,416 issued on Mar. 19, 1985 to the assignee of this application.
In the prior art, undesired play occurred as the guide pins and bores began to wear. Unfortunately, replacing the guide pins was not sufficient and the bores also required repair, resulting in costly repairs and lengthy downtime of the press. For example, the bores were typically repaired by welding them and then drilling the bores to the desired diameter so that the same size guide pins could be used. Alternatively, the bores were drilled to a larger diameter so that oversized guide pins could be used. Both of these repairs were undesirably time consuming and costly.